This invention relates generally to a device for producing airflow disturbances, and more specifically, to an aerodynamic spoiler mounted on the upper forward surface of the fuselage of an aircraft equipped to be refueled while in flight for masking or reducing the flow disturbances on the upper part of the fuselage caused by flow disturbances generated by the refueling boom.
One problem which has been encountered in aerial refueling operations involves pitch instability in the aircraft receiving fuel. These instabilities have been particularily noted where the receiving aircraft has its refueling receptacle located on the upper forward part of the fuselage and occur when the receiving aircraft moves in the close proximity to the refueling boom. As the aircraft and the boom come into close proximity during hook-up, the aircraft begins to oscillate in pitch, causing a considerable and, in some cases, unacceptable increase in workload for the pilot. A previous solution to the problem has been to modify the autopilot by adding special modes for use during refueling. This solution however, is somewhat expensive and does not totally eliminate the fluctuations.
In an effort to more precisely define the nature of the problem a flight test program was conducted with a particular jet transport aircraft, having a refueling receptacle in the nose section just forward of the cockpit. In the tests, a number of tufts were attached to the nose in the vicinity of the refueling receptacle and on the roof of the cockpit aft of the windshield. When the aircraft was brought in the close proximity of the refueling boom, it was noted that the tufts in the vicinity of the receptacle remained smooth, but that those on the cockpit roof showed significant activity. Such activity by the tufts was an indication that the airflow in that area had been disturbed. It was also found that the extent of the area in which disturbance occurred depended to some degree upon the relative position of the receiving aircraft with respect to the refueling aircraft during refueling.
The practical effect of this flow disturbance was to cause a decrease in the lift over that portion of the fuselage where the disturbance occurred and resultant nose-down moment on the aircraft. Because the lift loss and nose-down moment varied with the relative positions of the two aircraft, pilots found it quite difficult to stabilize or trim the receiving aircraft during refueling.
After reviewing the flight test data, the Applicants concluded that the flow disturbance was in all probability caused by turbulence from the boom. They also felt that an aerodynamic solution to the problem might be possible if a device could be mounted on the receiving aircraft which would either (a) generate a flow disturbance large enough to mask the disturbance caused by the boom, or (b) tend to reconstruct the flow over the cabin roof. With these two objectives in mind, four species of the present invention were conceived, and the effectiveness of each was verified by wind tunnel testing.
Accordingly, it is an object of this invention to provide for an aerodynamic means for eliminating pitch instabilities in an aircraft receiving fuel during aerial refueling. Another object of this invention is to provide for an aerodynamic means of producing flow disturbances and/or flow separation on the upper forebody of an aircraft receiving fuel during aerial refueling in order to mask the effect of turbulence from the refueling boom. A further objective of this invention is to provide for an aerodynamic means for reducing the flow disturbance over the upper forebody of the receiving aircraft initiated by turbulence from the refueling boom.